High temperature oxygen separation for the sulphur family of thermochemical cycles – Part II: Sulphur poisoning and membrane performance recovery

Voltage pulsing for performance recovery of yttria-stabilised zirconia membranes in oxygen/sulfur dioxide separation

“…Application of a DC voltage pulse was investigated and a 2 min pulse was found to partially recover membrane performance [3]. Preliminary results using a much shorter pulse of 1 s also showed performance recovery.…”

“…Process simulations showed that utilising a membrane to selectively remove oxygen from the decomposition reactor could increase the yield from 62.3% to over 90% at 1000 K [1]. An 80% conversion of SO 3 to SO 2 is obtained at 850 C theoretically if no oxygen is removed from the products. However, the temperature of the same conversion reduces to about 750 C if 90% of the oxygen is removed, and to around 590 C when 99.9% of the oxygen is removed [2].…”

“…Yttria-stabilized zirconia (YSZ), a ceramic with high oxygen ion conductivity, was proposed to separate oxygen from the products of sulfuric acid decomposition reaction. In our previous research, the feasibility of applying high temperature oxygen separation using YSZ membrane to the sulfuric acid decomposition process was investigated [1], and the performance of Pt/8YSZ/Pt membrane exposed to gas mixtures of SO 2 eO 2 eHe on the feed side was investigated at 850 C [3].…”

“…In the past few decades, extensive efforts have been devoted to characterizing sulfur poisoning behaviour of conventional electrodes (Pt is used as the electrode material here, however similar behaviour is seen with Ni electrodes used in many SOFC configurations), unravelling the mechanism of sulfur poisoning, and developing methods to reduce the degradation in performance. Sulfur poisoning of the cathode is characterized by a rapid initial drop in current upon exposure to sulfur dioxide (type I degradation), followed by a much slower but still significant rate for a long period of time (type II degradation) [3,4]. It is well accepted that type I degradation is caused by the dissociative adsorption of sulfur species around three-phase boundaries (the active sites for the electrochemical reactions) [4e8].…”

“…In previous work, platinum sulphite was observed on the cathode surface after SO 2 exposure by using surface analysis techniques (XRD, SEM-EDS and Raman Spectroscopy) [3].…”